Multilayer ceramic capacitor with terminal formed by electroless plating

ABSTRACT

A terminal to, most commonly, a ceramic capacitor, most commonly a multilayer ceramic capacitor (MLCC), is formed by electroless plating, also known as electroless deposition or simply as electrodeposition. In the MLCC having a multiple parallel interior plates brought to, and exposed at, at least one, first, surface, an electrically-conductive first-metal layer, preferably Cu, is electrolessly deposited upon this first surface directly in contact with, mechanically connected to, and electrically connected to, the edges of these interior plates. Lateral growth of the electrolessly-deposited first-metal is sufficient to span from exposed plate to exposed plate, electrically connecting the plates. One or more top layers, preferably one of Ni and one of Sn and Pb, are deposited, preferably by plating and more preferably by electrolytic plating, on top of the electrolessly-deposited Cu.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. patent applicationSer. No. 10/267,983, entitled MULTILAYER CERAMIC CAPACITOR WITH TERMINALFORMED BY ELECTROLESS PLATING, filed on Oct. 7, 2002, the disclosure ofwhich is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention generally concerns the fabrication of terminals onceramic capacitors, and the terminals so fabricated.

The present invention particularly concerns (i) the fabrication ofterminals on and to ceramic capacitors by process of plating wherelateral growth of the plating electrically connects exposed electrodes,and more preferably by process of electroless plating (also known aselectroless deposition or electrodeposition); and (ii) ceramic capacitorterminals having multiple plated or electrolessly plated (also known aselectrolessly deposited) layers.

BACKGROUND OF THE INVENTION

2.1 General Background

The capacitor is an electrical charge storage device and is one of thebasic building blocks in electronics. Capacitors are made in many typesincluding ceramic, tantalum, aluminum electrolytic, and film. Thepreferred embodiment of the terminal fabrication method of the presentinvention will be seen to be specific to ceramic capacitors. However,the terminal fabrication method of the present invention will be seen tobe extendable to other electronic components, such as inductors, otherthan just capacitors.

Ceramic capacitors cover a wide range of applications including: chargestorage, DC blocking, circuit components coupling, AC by-pass, andtransient voltage suppression. See, e.g., Galliath, A. P., NovacapTechnical Brochure, website <http:\www.novacap.com>, 2001. The challengefor the ceramic capacitor manufacturer is the same for any manufacturer:reduce costs and increase yields. Worldwide production of ceramiccapacitors range in many billions of capacitors annually. See ElectronicIndustry Association, Market Data Book, 1987. The selling price, circa2002, on some smaller capacitors is on the order of 1000 capacitors perUnited States dollar. To remain competitive many manufacturers areturning to new technology to reduce costs.

Traditionally ceramic capacitors require the use of precious andsemiprecious metals, typically palladium and silver for electrodes aswell as end terminals. In the past five years, the cost of palladium hasbeen extremely volatile. The cost per troy ounce has fluctuated fromunder than $200 to over $1000 U.S. See Palladium (NYMEX): Monthly PriceChart, website <http:\futures.tradingcharts.com/chart/PA/M> on theInternet circa 2002. This has led to a strong push in the development ofceramic materials that use base metal electrodes such as copper andnickel. See Mistler, R. E., Twiname, E. R., Tape Casting Theory andPractice, The American Ceramic Society, 2000. Likewise, there has been astrong push in process improvement and automation in order to improveyields and reduce fabrication time.

The present invention will be seen to concern the terminating of ceramiccapacitors, a process where end terminals of metal are applied toceramic bodies containing electrodes. The present, circa 2002,industrial method for realizing these electrodes uses thick film cermetpastes. See Galliath, A. P., Novacap Technical Brochure, website<http:\www.novacap.com>, 2001. More regarding this method will bediscussed in section 2.8, below.

2.2 The Basic Capacitor

The basic capacitor is a charge storage device composed of an insulatorsandwiched between two conductors, as shown in FIG. 1. See Galliath, A.P., Novacap Technical Brochure, website <http:\www.novacap.com>, 2001.The intrinsic properties of the dielectric material determine thecharacteristics of the capacitor. Some of these characteristics includecapacitance, insulation resistance, and dielectric strength.

Capacitance is measured in Farads. A Farad is defined as one Coulomb perVolt. A Farad is a relatively large amount of charge, so it is morecommon to use units such as micro-Farad (μF), nano-Farad (nF), andpico-Farad (pF).

Dissipation factor, DF, is defined as the loss tangent in an AC circuit.See Harper, C. A., Handbook of Thick Film Hybrid Microelectronics,McGraw-Hill, New York, 1974. For simplicity, DF can be defined as theloss factor. The ideal capacitor, in which the dielectric would exhibitinfinitely high resistance, would have a loss factor of zero. Thus oncea charge has been applied the ideal cap would hold that charge withoutany loss. Two main factors contribute to the DF of ceramic capacitors.The first is an intrinsic property of the ceramic, dielectricabsorption, and the second is the equivalent series resistance (ESR)associated with all the electrical connections involving the cap.Sources of ESR include resistivity of the electrodes, connectionsbetween the electrodes and terminals, and solder connections to printedcircuit boards (PCBs). Connections between electrodes and terminals areof primary interest to the present invention. A capacitor has adissipation factor, or DF; the equivalent circuit for which is wellknown. Dielectric absorption is represented as a resistor connectedparallel to the capacitor, and an equivalent series resistance, or ESR,is represented as a resistor in series with the capacitor.

Insulation resistance (IR) is a measure of the dielectric material'sability to block DC current flow when a DC bias is applied. Thisrelationship may be plotted, and IR is commonly used instead of R todifferentiate between a capacitor and a resistor. For ceramicdielectrics, the IR is very high and is typically expressed in terms of10⁶ or 10⁹ ohms. The IR for ceramic capacitors is typically measured atthe rated working voltage, and the IR values can be on the order of 10¹²ohms.

Dielectric strength is a measure of the ceramic's ability to withstand ahigh bias without electrical breakdown and is typically expressed interms of volts per mil or volts per micron of thickness. If an appliedvoltage is steadily increased, then at a certain point the applied fieldwill become be high enough to drive free electrons between the twoconductor plates. The heat generated will then result in a breakdown ofthe dielectric layer. In ceramic capacitors, dielectric breakdownresults in the catastrophic failure of the cap. The typical ceramic capcan exhibit dielectric strength on the order of 1000 volts per mil or 40volts per micron.

2.3 Ceramic Capacitors

Ceramic capacitors are available in a wide array of capacitance values,working voltages, sizes, and for various applications. Capacitancevalues are available from less than one pico-Farad to hundreds ofmicro-Farads. There is no real maximum value since capacitance can beadded by putting two or more capacitors in parallel. Working voltagesare available from less than 10 VDC to over 10,000 VDC. Typical sizesrange from size “0201” and up. The 0201 size code indicates a part thatis nominally 0.020 inch long, 0.010 inch wide, and up to 0.010 inchthick. In many cases, manufacturers will make the thickness equal to thewidth in order to maximize capacitance and for ease of handling. Ceramiccapacitors are available for various applications, and ceramicdielectrics have been formulated to meet these applications. Somedielectric formulations maximize capacitance while others are bestsuited for high voltage applications. Some formulations function best atcryogenic temperatures while others will perform at 200° C. or more. Dueto their versatility, ceramic capacitors are found in virtually allelectronic applications from household electronics to medical implantsto space and military applications.

2.4 MLCC Construction

Multilayer ceramic capacitors (MLCCs) are manufactured by interleavingmultiple layers of ceramic dielectric and metal electrodes, as shown inFIGS. 2A-2C. The layer thickness (t), also referred to as electrodespacing, is generally proportional to the voltage rating of the cap.Depending on the voltage rating, the layer thickness can be less than 10μm or much thicker for high voltage applications. Each layer of an MLCCis in effect a single capacitor. When the electrodes are electricallyconnected with a metallic end terminal then the result is the summationof the capacitance from all the individual layers.

2.5 End Terminals

The end terminals electrically connect together each of the two opposingsets of electrodes of the capacitor and serve as terminals forelectrical connections to PCBs. The typical end terminal material is athick film cermet paste, usually composed of either Ag powder or Pd—Agpowder and glass frit. The terminals are formed by dipping the MLCC intothe thick film paste and sintering the paste in the range of 600°C.-800° C. This does not affect the ceramic chip since the unterminatedMLCC is processed at 1100° C.-1300° C. Sintering causes the glass fritto adhere to the ceramic. The metal powder also forms a diffusion bondto the electrodes, thus making electrical connections to the metalelectrodes.

The dipping process creates end terminals that wrap around all foursides of the capacitor. The wrap-around structure is necessary for goodadhesion to the ceramic body. Terminal adhesion strength is typicallyhigher than the tensile strength of the ceramic. Terminals with minimalwrap-arounds tend to have lower adhesion strength and would besusceptible to peeling.

Once terminated, a MLCC is typically electroplated with nickel and thentin or tin-lead solder in order to be surface-mountable.Surface-mounting is the soldering of components onto PCBs. See Prassad,R. P., Surface Mount Technology Principles and Practice, Van NostrandReinhold, New York, 1989. The nickel layer is typically referred to asthe barrier layer. Although nickel is solderable it does not readilydissolve in molten solder as silver does. The nickel layer functions asa protective barrier for the silver end terminals when the capacitorsare soldered to PCBs. Tin and tin-lead coatings serve to protect thenickel from oxidation and to make components readily solderable. FIG. 4Ais a cross-sectional micrograph of a silver terminal that has beenplated with nickel and tin-lead.

2.6 Plating of End Terminals

Typically, end terminals are electrolytically plated with a layer ofnickel followed by a layer of tin, tin-lead, or gold. The traditionalmethod to plate ceramic capacitors is barrel plating. Barrel plating isthe process in which parts are placed in a rotating mesh basket,typically made of polypropolene, and immersed in a plating bath as shownin FIG. 6. See Singleton, R. Barrel Plating, Metal Finishing Guidebookand Directory, 2001, p. 340-359,

2.7 Improving MLCCs

As mentioned in Section 2.1 there is ongoing materials development inthe ceramic capacitor industry in order to reduce costs. In the past 30years over 500 patents relating to ceramic capacitors have been issuedin the United States. These patents cover every aspect manufacturing,and in the last 5 to 10 years much effort has been going towardscreating ceramics that can be processed using inexpensive metals forelectrodes.

The cermet method of forming end terminals described in Section 2.5 hasbeen the industry standard for many years. There has been muchimprovement in quality of the terminals; however, the basic compositionremains a paste of metal powder and glass frit. There has been littlework on an alternative method to form MLCC terminals. About a dozenpatents are related to end terminals. Three of these patents involvedalternative methods terminating MLCCs. All three processes use cermetpastes.

Westwater showed that sputtered terminals would reduce board space. SeeWestwater, R., Sputtered Terminations Gain Space, ElectronicEngineering, vol. 65, August 1993, p. 31.

Scrantom also patented a sputtering process of applying terminals toceramic bodies. See Scrantom D. G., Hopkins L., Method of ApplyingTerminations to Ceramic Bodies, U.S. Pat. No. 4,561,954, 1985.

The importance of board space reduction will be discussed in Section3.3. Sputtered terminals do help to reduce board space; however, it islikely that this method would make parts more costly to produce.

The present invention teaches forming terminals onto bare MLCCs usingelectrodeposition. In 1974 Hurley patented a method of terminatingceramic capacitors where a thin film of immersion gold is deposited ontothe electrode edges prior to applying termination paste. See Hurley T.P., Multilayer Ceramic Capacitor and Method of Terminating, U.S. Pat.No. 3,809,973, 1974. The capacitors used in Hurley's method have basemetal electrodes, and the gold film prevent oxidation of the electrodesduring sintering in air.

2.8 Specific Prior Patents

Other United States patents of relevance to the present inventioninclude the following.

U.S. Pat. No. 3,665,267 to Acello for CERAMIC CAPACITOR TERMINALS showsbond pads to a ceramic capacitor that are soldered. A monolithicmulti-electrode capacitor chip has silver electrode pickups on opposededges of the capacitor stack. A multi-metal clad strip is affixed on thesilver pickup, therein affording a smooth compatible terminal surfacefor further bonding purposes as the capacitor is used in hybridcircuitry.

U.S. Pat. No. 4,246,625 to Prakash for a CERAMIC CAPACITOR WITH CO-FIREDEND TERMINATIONS shows co-fired terminations. A ceramic body containingembedded metal electrodes is provided with end terminationconfigurations using a paste containing base metal particles, glass fritand MnO₂; the body and end terminations being co-fired to provide aceramic capacitor.

U.S. Pat. No. 4,293,890 to Varsane for a CERAMIC CAPACITOR WITH ENDTERMINALS shows a leaded capacitor. A lead wire for a miniaturecapacitor having a U-shaped clamp at one end and being removablyattached to a carrier, such as a sprocketed ribbon, at the other end.Each of the U-shaped clamps grasps and holds a terminal end of thecapacitor. The carrier is used with conventional geared wheels and reelsto move the capacitors and lead wires from station to station duringtheir assembly procedure. When assembly is completed, the leads can beremoved from the carrier.

U.S. Pat. No. 4,346,429 to DeMatos for a MULTILAYER CERAMIC CAPACITORWITH FOIL TERMINAL shows a special style of terminal. Namely, a ceramiccapacitor has a metal foil terminal strip configuration to reduce highfrequency inductance.

U.S. Pat. No. 4,517,155 to Prakash, et al. for a COPPER BASE METALTERMINATION FOR MULTILAYER CERAMIC CAPACITORS shows copper endterminations. These terminations—reportedly of excellent electrical andmechanical properties—are provided on multi-electrode ceramic capacitorsby applying copper, glass frit metallizations to the ends of a ceramiccapacitor and firing the applied metallization in an atmosphere ofnitrogen which contains a controlled partial pressure of oxygen.

U.S. Pat. No. 4,561,954 to Scrantom, et al. for a METHOD OF APPLYINGTERMINATIONS TO CERAMIC BODIES concerns sputtered terminals. A method ofterminating a multilayer ceramic capacitors and like electroniccomponents is disclosed. In accordance with the method the capacitorsare loaded into apertures formed in an elastomeric mask such that onlythe surface portions to be metallized are exposed. In advance ofloading, the surfaces of the mask are pre-coated, preferably by asputtering procedure, so as to preclude “out-gassing” of the maskmaterial during sputtering.

U.S. Pat. No. 4,571,276 to Akse for a METHOD FOR STRENGTHENINGTERMINATIONS ON REDUCTION FIRED MULTILAYER CAPACITORS concerns themetallurgy of capacitor terminals. The strength of end terminations onmultilayer capacitors employing base metal electrodes is increased byheating the terminations, subsequent to firing in a reducing atmosphere,in an atmosphere in which the oxygen partial pressure is at least equalto that of air for a period of at least 15 minutes at a temperature of375° C.-600° C.

U.S. Pat. No. 4,757,423 to Franklin for a FUSE FOR ELECTRONIC COMPONENTdoes not concern a capacitor, but does describe how the technique ofapplying metal-coated polymer particles dispersed in a resin binder as aconductive paste, a variant upon the common method of creating aterminal for a ceramic capacitor, may be used for a fuse. In theFranklin patent a solid electrolytic capacitor has an anode body and ananode wire and lead out connections. In series with the connections andthe body is a fusable link formed of a composite of low melting pointconductive plastics metal matrix. The fusable link is in the form of apad of this material. In a preferred form this material is made bycompressing into sheets metal-coated polymer particles. The sheet is cutinto pads and inserted into the capacitor assemblies to act as acombined thermal and electrical fuse. Preferably the pads are less than1 mm thick and coated on both sides with solder and approximately 1 mmsquare. The pads can be reflow soldered between the anode and the leadframe or negative wire termination. Alternatively it can be reflowsoldered between the anode wire and the positive wire termination. Asthe current reaches high level if a fault develops in the capacitor, themetal layer will melt and also melt the plastics. The metal will thendisperse in the liquid plastics and on cooling will not re-establishconduction because it is no longer in the same physical form.Alternatively the fusible link comprises metal-coated polymer particlesdispersed in a resin binder and applied as a conductive paste.

U.S. Pat. No. 4,806,159 to De Keyser, et al. for an ELECTRO-NICKELPLATING ACTIVATOR COMPOSITION, AND METHOD FOR USING A CAPACITOR MADETHEREWITH shows a plating, and plating activator, composition. A platingactivator composition that is largely silver is applied in a thin filmto two surface areas of a ceramic chip capacitor. Subsequently, manysuch chip capacitors are electrolytically nickel plated, e.g. areelectro-nickel barrel plated to provide two strongly adhered nickelterminals to the component. This activator composition consistsessentially of at least 85% Ag, from 0.1 to 7% Pd, from 1% to 10% of anelement selected from Cu, Si, Bi, Zn, Fe, Ni, Sn, Zr, Nb, Sb, Mn andcombinations thereof. The terminals are alleged to be strong, trulyconformal and are highly manufacturable.

U.S. Pat. No. 4,881,308 to McLaughlin, et al. for a METHOD OFTERMINATING LEAD FILLED CAPACITOR shows the use of lead in capacitorterminals. A method of manufacturing a ceramic capacitor of the leadfilled type includes coating the ends of the ceramic monolith with aterminating paste incorporating oxidizable metal particles characterizedin that the lead will not wet to oxides of the metals but will wet toun-oxidized or lightly oxidized increments of the metals. The paste isfused in an oxidizing environment or is fused in an inert environmentand thereafter heated in an oxidizing environment with the result thatthe metal increments adjacent the exterior of the fused coating areoxidized whereas the metal at the interior portions of the paste areun-oxidized or only slightly oxidized. Upon metal injection, the leadwill wet to the interior portions of the fused paste but will not wet tothe exterior of the paste whereby injected chips may be readilyseparated and whereby the size of the chip is rendered predictable dueto the absence of adherent lead.

U.S. Pat. No. 5,363,271 to Pepin for THERMAL SHOCK CRACKING RESISTANTMULTILAYER CERAMIC CAPACITOR TERMINATION COMPOSITIONS describes atermination paste. A thick film conductor composition suitable for usein forming terminations for titanate-based MLCs comprises finely dividedparticles of: (a) electrically conductive precious metal, and (b) metaloxide-based glass having a Dilatometer softening point of 400° C.-700°C. The (b) metal-based oxide glass preferably consists of at least oneglass modifier having an ionic field strength higher than the ionicfield strength of the titanate cation, both (a) and (b) being dispersedin an organic medium.

U.S. Pat. No. 5,670,089 to Oba, et al., for a CONDUCTIVE PASTE FOR MLCTERMINATION concerns the use of conductive paste in the terminals of amultilayer capacitor (MLC). The purpose of the invention is to provide aterminal electrode composition for a multiple-layered capacitor that issuitable for a plating base and that has improved resistance to heatstress as the result of sintering at a low temperature (highreliability). The terminal electrode composition particularly for amultiple-layered capacitor of this invention is made of precious metalparticles and 0.5-7 wt. % (based on the weight-of the precious metalparticles) of an inorganic binder having a 400° C.-500° C. glasstransition point and a 400° C.-550° C. glass softening point.

SUMMARY OF THE INVENTION

The present invention concerns a method for applying end terminals toceramic capacitors for purposes of making areas to which electricalcontact may subsequently be made, most commonly electrical conduct bysoldering. The method of the present invention is an alternative to thepresent, circa 2002, industrial method using thick film cermet pastes toform the terminals of ceramic capacitors.

The present invention contemplates the creation of terminals to ceramiccapacitors by process of plating where lateral growth of the platingelectrically connects exposed electrodes, thus a sort of “platingintentionally laterally extended”. Being that this lateral growth isdifficult to realize with conventional electrolytic plating, the presentinvention particularly contemplates the creation of terminals uponceramic capacitors by process of electrodeposition, commonly referred toas electroless plating or sometimes simply, but imprecisely, as plating.By using an electrodeposition method ceramic capacitors can beterminated using commercially available plating solutions without eitherexpensive tools or automated equipment.

Ceramic capacitors so having electroless plating so as to electricallyconnect exposed electrodes for purpose of terminal formation can also bequite easily subsequently electroplated in regions of the terminal. Theresultant ceramic capacitor thus has a terminal of multiple layers, allof which layers are preferably in some form plated. Alternativelyexpressed, the present invention specifically contemplates a multilayerceramic capacitor having an end terminal made at least in part byprocess of electroless plating, also known as electroless deposition orsimply as electrodeposition.

In broad terms the present invention is embodied in a ceramic capacitorhaving a terminal that comprises electroless plating. [Note that theword “plating” occurs as both a verb and a noun in this specification.]

1. The Structure of a Ceramic Capacitor With a Plated Terminal inAccordance With the Present Invention

A capacitor adapted to the present invention is commonly a multilayertype with multiple planar interior plates brought to, and exposed upon,a first surface. In this instance the preferably electrolessly-platedterminal of this multilayer capacitor is directly in contact with,mechanically connected to, and electrically connected to, the multipleinterior plates at the locations where each interior plate is exposedupon the first surface. The electroless plating on each surface issufficiently extensive so as to electrically connect (if desired) all ofthe multiple interior plates, or electrodes, of the multilayer capacitorthat are brought to, and exposed at, the exterior surface.

This point is important, and as significant as is the plating, orelectroless plating, itself. Namely, the plating, or electrolessplating, extends laterally so far so as to electrically connect theexposed edges of the interior plates, or electrodes, that appear uponthe surface of the ceramic capacitor.

Although more economical, and quite strong, the electrolessly platedlayer does not intrinsically adhere quite so strongly as is does a metallayer formed from cermet paste by methods of the prior art. Thereforethe present invention still further contemplates that mechanical andelectrical contact via electroless plating should be made not merelyupon one surface of the ceramic capacitor, but should “wrap over” one orboth edges onto adjacent side surfaces of the capacitor.

Still furthermore, layers and sides where no interior plate wouldnormally be exposed—the interior plate of this layer most normally beingexposed an connected upon an opposite side—may be made with small,short, “stub” plates. These “stub” plates do not appreciably affect thecapacitance. The “stub” plates, exposed on the surface just as are theinterior electrode plates, present yet further metal to which theelectrolessly plated layer can, and will, adhere.

The net result of the most preferred embodiments of the presentinvention is not merely a functioning ceramic capacitor of lower cost,but one that is just as strong (or very nearly as strong, depending upondetails of construction) and that meets the exceptionally high andrigorous failure and reliability criteria of existing ceramiccapacitors.

2. One Detailed Aspect of A Most Preferred Embodiment of a MultilayerCeramic Capacitor in Accordance with the Present Invention

A most preferred embodiment of a multilayer ceramic capacitor inaccordance with the present invention is in the shape of aparallelipiped body. In this capacitor the multiple interior plates arenot only brought to, and exposed at, a first surface, but also at aportion of at least one, adjoining, second surface of the capacitor atan edge region where this second surface joins the first surface. Themultiple interior plates are thus exposed “on two sides of an edge”, andthe electroless plating extends “over the edge”. By this constructionthe electroless plating occurs not only upon the first surface so as tothere contact, and mechanically and electrically connect, a number ofinterior plates, but also wraps over an edge of the capacitor from thefirst surface onto the portion of the at least one second surface. Atthis portion of the at least one second surface the electroless platingis again directly in contact with, and mechanically and electricallyconnected to, the interior plates.

This preferred contact on both sides of an edge serves is so as toenhance the mechanical strength with which the electroless platingadheres to the exposed edges of the electrode plates. So also will aterminal subsequently made upon the electroless plating by the additionof one or more metal layers on top of the electroless plating adherestrongly, and well, to the interior plates, and to the ceramic body, ofthe multilayer capacitor.

The present invention further contemplates a multilayer ceramiccapacitor that is optimized in the shape of its interior plates, orelectrodes, to accept end termination with, by and through a terminalthat is formed at least in part by electroless plating (also know aselectroless deposition or electrodeposition). In this preferredmultilayer ceramic capacitor multiple parallel interior plates that arebrought to a first surface are also brought to, and exposed at, aportion of at least one adjoining second surface of the capacitor. Thesecond surface portion where the interior plates are exposed is wherethe second surface meets the first surface. The electrically-conductivelayer then electrolessly-deposited accumulates not only upon the firstsurface so as to there contact, and mechanically connect, andelectrically connect the plurality of plates, but also wrap over an edgefrom the first surface onto the portion of the at least one secondsurface. At this location it yet again contacts, and mechanically andelectrically connects, to the interior plates. The contact on twosurfaces adds physical strength to the electrolessly-deposited layer,ensuring against this layer becoming detached from the ceramic body andfrom the electrical plates of the multilayer capacitor.

3. Another Detailed Aspect of A Most Preferred Embodiment of aMultilayer Ceramic Capacitor in Accordance with the Present Invention

In one of its most preferred embodiments, a multilayer capacitor inaccordance with the present invention incorporates within its body—inaddition to a first plurality of interior “electrode” plates havingtheir edges exposed at one, first, surface and another, normally equal,second plurality of interior “electrode” plates having their edgesexposed at an opposite, second, surface—first, and preferably alsosecond, pluralities of short, “stub”, plates. These “stub” plates arelocated upon alternate layers from the “electrode” plates that arebrought to, and exposed at, the same surface. They proceed only butslightly into the interior of the ceramic body of the capacitor.

The purpose of the “stub” plates is not to affect capacitance. After theelectrodeposited layer, and terminal, is affixed these stub plates willhave but little effect on capacitance, and mostly affect the fringingcapacitance, arguably serving to very slightly increase it in abeneficial manner.

The purpose of the “stub” plates is to expose yet further metal to whichthe electrolessly deposited metal will adhere. They also serve to makeit easier that electromigration of the deposited metal proceedingoutward from each plate—both “electrode” and “stub” types—should soon,evenly and reliably contact the next adjacent plates.

Neither the (i) “wrap over” electroless deposition discussed in section1 above, nor the (ii) “stub” plates discussed in this section 2, arenecessary to make a fully functioning ceramic capacitor with an endterminal that is at least in part electrolessly deposited in accordancewith the present invention. Instead, it should be understood that theseoptional features are directed to making a new ceramic capacitor that,while differing in an essential fabrication step from convention, can beboth (i) tested and (ii) predicted to meet the laudably high reliabilitystandards of its predecessors.

4. A Multilayer Ceramic Capacitor with a Termination Including anElectroless-plated Electrically-conductive Metal Layer

Therefore, in one of its aspects the present invention is embodied in amultilayer ceramic capacitor with a termination including anelectroless-plated electrically-conductive metal layer.

Specifically, a multilayer ceramic capacitor that has a number ofparallel interior plates which are brought to, and exposed at, at leastone, first, surface of the capacitor for purpose of electricaltermination, is supplied with an electrically-conductive first-metallayer by process of electroless plating (also known as electrolessdeposition or electrodeposition). The electrolessly-deposited layer is(1 a) directly in contact with, (1 b) mechanically connected to, and (1c) electrically connected to, the interior plates where each is exposedupon the first surface. It is sufficiently extensive so as toelectrically connect the plurality of plates.

The electrolessly-deposited first-metal layer may be identified bycharacteristics familiar to materials scientists familiar withelectroplating. Namely, this electrolessly-deposited first-metal layeris characterized for showing lateral growth of anelectrolessly-deposited first-metal from an edge, exposed at the firstsurface, of a first one of the plurality of interior plates to anexposed edge of a next, second, one of the plurality of interior platesthat is likewise exposed at the first surface. Meanwhile, theelectrolessly-deposited first-metal likewise grows laterally from theexposed edge of the second interior plate towards the exposed edge ofthe first interior plates. These exposed edges are quite close together,preferably less than 0.01 inches (<0.01″) in separation. (The separationof the edges of the interior plates is commonly the same as theseparation between the plates interior to the multilayer ceramiccapacitor.) The span of lateral growth is sufficient to span this gap,and is sufficiently extensive so as to contact all the plates. Theelectrolessly-deposited first-metal thus serves to electrically connectthe interior plates.

In a most preferred multilayer ceramic capacitor having a plurality ofparallel interior plates brought to, and exposed at, at least one,first, surface of the capacitor for purpose of electrical termination,these same interior plates are preferably also brought to, and exposedat, a portion of at least one second surface of the capacitor at aregion where this second surface meets the first surface.

The electrolessly-deposited electrically-conductive layer is thuselectrolessly-deposited not only upon the first surface so as to (1 a)contact, and to (1 b) mechanically connect, and to (1 c) electricallyconnect the plurality of interior plates, but also so as to wrap over acorner from the first surface onto the portion of the at least onesecond surface where the electrolessly-deposited electrically-conductivelayer again also (1 a) contacts and (1 b) mechanically connects and (1c) electrically connects to the plurality of interior plates.

Also in a most preferred multilayer ceramic capacitor having a pluralityof parallel interior plates brought to, and exposed at, at least one,first, surface of the capacitor for purpose of electrical termination,yet another, second, plurality of plates, called stub plates, are both(i) interspersed between the multiple interior plates and (i) extendslightly into the ceramic of the ceramic capacitor at the first surface.These stub plates serve to present at the first surface additionalexposed edges of metal to which the electroless plating adheres. By thisadditional connection the separation strength of the electroless platingfrom the ceramic of the ceramic capacitor is augmented; the electrolessplating adhering to the exposed edges of the stub plates as well as tothe exposed edges of the interior plates.

The electrolessly-deposited electrically-conductive first-metal layerpreferably consists essentially of copper (Cu), but may also consist ofnickel (Ni), or of copper (Cu) in combination with nickel (Ni).

The multilayer ceramic capacitor preferably further includes, on top ofthe electrolessly-deposited electrically-conductive layer, asecond-metal layer of electrically-conductive second metal. Thissecond-metal layer is plated, either again by process of electrolessdeposition, or, more preferably and more conventionally, by electrolyticplating. If electrolessly plated (electrolessly deposited), thesecond-metal layer is again characterized, as was the first metal layer,in that lateral growth of the electrolessly-deposited second-metal isextensive. Namely, it is sufficiently extensive so as to cover theelectrically-conductive first-metal layer (that was also electrolesslydeposited).

Any electrolessly-, or electrolytically-, depositedelectrically-conductive second-metal layer preferably consistsessentially of nickel (Ni).

The most preferred multilayer ceramic capacitor still further has, ontop of the electrically-conductive second-metal layer, yet a third-metallayer of electrically-conductive third metal.

This third-metal layer is again plated, but this time stronglypreferably only by, and with, electrolytic plating. Theelectrolytically-plated electrically-conductive third-metal layerpreferably consists essentially of tin (Sn) in combination with lead(Pb).

5. A Method of Fabricating a Terminal of a Ceramic Capacitor byElectroless Plating

In yet another of its aspects, the present invention is embodied in amethod of fabricating a terminal of a ceramic capacitor by electrolesslyplating the ceramic capacitor

Specifically, given a multilayer ceramic capacitor with a number ofinterior plates having edges that are exposed upon at least one, first,surface of the ceramic capacitor, the method consists of electrolesslydepositing a layer of conductive first metal directly onto the at leastone surface where the edges of the plates are exposed.

This electrolessly depositing of the layer of conductive first metal maybe, and preferably is, further, and also, onto at least a portion of atleast one second surface of the capacitor where this second surfacemeets the first surface and where the interior plates are also exposed.

The electrolessly depositing is of a layer of conductive first metalpreferably consisting of copper (Cu), but potentially also nickel (Ni),or copper (Cu) in combination with nickel (Ni).

Another, second, layer of electrically-conductive second-metal ispreferably deposited on top of the electrolessly-depositedelectrically-conductive first-metal layer. This second-metal layer ispreferably so deposited by process of plating, which can again beelectroless plating or, more preferably, electrolytic plating.

The preferably plated electrically-conductive second-metal layerpreferably consists essentially of nickel (Ni).

Still further in the preferred method, a third-metal layer ofelectrically-conductive third metal is deposited on top of theelectrolessly-deposited electrically-conductive second-metal layer. Thedepositing is yet again by plating, and strongly preferably byelectrolytic plating. The plated electrically-conductive third-metallayer preferably consists essentially of tin (Sn) in combination withlead (Pb).

6. A Ceramic Capacitor Having A Terminal That is Plated

In yet another of its aspects, it may be considered that the presentinvention is embodied in a terminal of a ceramic capacitor that isdistinguished not only for preferably being electrolessly plated, butfor being plated in the first instance, and in any manner, where theplating undergoes lateral growth. This lateral growth is mandatory, andmust extend so far so as to permit electrical connection betweenadjacent ones of the internal plates, or electrodes, or the capacitorwhere brought to, and exposed at, the surface of the capacitor.

In this aspect the present invention is embodied in a ceramic capacitor.conventionally having electrodes exposed upon at least one surface, anda terminal connecting the exposed terminals. In accordance with thepresent invention the terminal is plated so that lateral growth of theplating connects adjacent ones of the electrodes where the electrodesare exposed upon the at least one surface. The terminal so exhibitinglateral growth may be either electrolytically, or, more preferably,electrolessly, plated.

Alternatively, the present invention may be considered to be embodied inthis conventional ceramic capacitor having electrodes exposed upon atleast one surface, and a terminal connecting the exposed terminals, saveonly that the terminal is distinguished by including multiple layers ofplating wherein the plating of at least one layer extends so far so asto connect adjacent ones of the electrodes at the locations where theseelectrodes are exposed upon the at least one surface of the capacitor.

The at least one plated layer that extends so far so as to connectadjacent ones of the electrodes at locations where the electrodes areexposed upon the at least one surface may be, as before, eitherelectrolessly, or electrolytically, plated.

These and other aspects and attributes of the present invention willbecome increasingly clear upon reference to the following drawings andaccompanying specification.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring particularly to the drawings for the purpose of illustrationonly and not to limit the scope of the invention in any way, theseillustrations follow:

FIG. 1 is a prior art showing of a basic capacitor.

FIG. 2A is a prior art showing of a standard design of an multi-layerceramic capacitor (MLCC); externally the MLCC is a monolithic ceramicbody with a metal terminal on each end.

FIG. 2B is a cross-sectional view of the MLCC in FIG. 2A showing theinterleaf construction of ceramic dielectric and metal electrodes.

FIG. 2C is a detailed view of a portion of FIG. 2B.

FIG. 3 is a prior art showing of a standard 0403 ceramic cap.

FIGS. 4A and 4B are a prior art cross-sectional micrograph showing adeposit of 90/10 tin/lead over nickel over silver termination.

FIG. 5 is a prior art showing of a standard set-up for electroplating.

FIG. 6 is a prior art showing of a barrel plating set-up; the parts andmedia together comprise the cathode.

FIG. 7 is a prior art showing of how inside a plating basket conductivespheres make electrical contact to capacitors; the spheres beingapproximately 0.5 mm diameter.

FIGS. 8A and 8B show the end of a capacitor with its electrodes exposed,which capacitor may be terminated with cermet terminals in accordancewith the prior art as in previous FIG. 7, or which may be terminatedwith electrolessly deposited terminals in accordance with FIGS. 9A-9C.

FIG. 9A shows a capacitor in accordance with the present invention wherecermet terminals of the prior art are replaced with electrodepositedterminals; in this configuration the terminals are rectangular bands anddo not wrap around on all sides as do the terminals shown in FIG. 2A.

FIG. 9B is a cross-section view of FIG. 9A.

FIG. 9C is a detailed view of a portion of FIG. 9B

FIG. 10A is an exploded cross-sectional view showing lateral growth ofthe nickel deposit which would electrically connect the electrodestogether.

FIG. 10B is a detailed view of a portion of FIG. 10A

FIGS. 11A-11E respectively show a side view of two standard capacitors;these capacitors separated by a gap to prevent electrical shorting; thespacing if there is no gap; and two EDTCs in accordance with the presentinvention spaced with no gap but incurring no shorting.

FIG. 12A is a diagram of the electroless plating of copper onto ceramiccapacitors.

FIG. 12B is Table 1 containing a summary, of a preferred platingprocedure of the present invention.

FIGS. 13A-13D are micrographs of the copper electrolessly deposited inaccordance with the present invention.

FIG. 14A-14D are micrographs of a nickel deposit.

FIG. 15 is a cross-sectional micrograph showing the nickel deposit wherethe wavy profile of the nickel deposit was expected.

FIG. 16A-16D, are micrographs showing a deposit of 90/10 tin/lead.

DETAILED DESCRIPTION

The following description is of the best mode presently contemplated forthe carrying out of the invention. This description is made for thepurpose of illustrating the general principles of the invention, and isnot to be taken in a limiting sense. The scope of the invention is bestdetermined by reference to the appended claims.

Although specific embodiments of the invention will now be describedwith reference to the drawings, it should be understood that suchembodiments are by way of example only and are merely illustrative ofbut a small number of the many possible specific embodiments to whichthe principles of the invention may be applied. Various changes andmodifications obvious to one skilled in the art to which the inventionpertains are deemed to be within the spirit, scope and contemplation ofthe invention as further defined in the appended claims.

1. Method of the Present Invention for Electrodeposited Terminals (EDTs)

Electrodeposition is, in accordance with the present invention, analternative method to using cermet pastes to create terminals on ceramiccapacitors. The method of the present invention (i) selectivelyelectrolessly plates onto the exposed electrodes and the (ii) grows theplated deposit to the desired thickness.

1.1 Challenges

To form the terminals on ceramic capacitors it is necessary toselectively deposit a metallic layer on the electrode ends of the capwithout depositing metal on the entire cap. FIG. 8A and FIG. 8B show oneend of the capacitor where a terminal must be deposited. The exposedelectrodes to be plated are metallic areas on the order of 1 mm long and1 μm wide. It would be impractical to attempt to electroplate the partsin this condition. In order to make electrical contact as shown in FIG.6 the conductive spheres would need to be on the order of 1 μm indiameter. Therefore, it would be necessary to enlarge the electrodesprior to electroplating.

Terminal adhesion is a major concern. Adhesion strength is importantboth for mechanical and electrical properties. As mentioned in Section2.5 of the Background of the Invention section of this specification,cermet terminals exhibit adhesion strength that is typically higher thanthe tensile strength of ceramic capacitors. Unlike cermet terminals,which employ glass frits for adhesion, the EDT of the present inventionrelies on adhesion to the exposed edges of the electrodes. The EDTs willneed to exhibit similar adhesion of the cermet terminals in order to becompatible with industrial applications.

Electrical reliability is also a concern. Electrodeposited terminalcapacitors (EDTCs) must be reliable in order to be an acceptablesubstitute for the standard part. Chen showed that the reliability ofceramic capacitors can be degraded after plating due to adsorbedhydrogen. See Chen, W., Influence of Nickel Plating on MultilayerCeramic Capacitors and the Implications for Reliability in MultilayerCeramic Capacitors, Journal of the American Ceramic Society, vol. 81,no. 10, Oct. 98, p. 2751-2752. Chen argued that adsorbed hydrogen candiffuse into the ceramic body and cause a reduction reaction whichincreases the free electron concentration. An increase of free electronswould lead to a decrease of insulation resistance and dielectricstrength as described in Section 2.2 of the Background of the Inventionsection of this specification.

The EDTC of the present invention may be more susceptible since theelectrodes will be exposed to the plating solution. With standardcapacitors the cermet terminals completely cover the electrodes.

1.2 Strategy of the Present Invention

The strategy can be divided into three steps. The first step is todesign the electrodes so that they are exposed on two sides of the MLCCas well as the ends. This method is sometimes used to lower theequivalent series resistance (ESR) of the capacitor. Here, theelectrodes exposed to the sides will provide the necessary wrap-around,as shown in FIGS. 9A-9C. The EDT wrap-around will only be on two sidesas opposed to all four sides. Reduced wrap-around will likely result inreduced terminal strength. However, the two-side wrap-around does havean advantage over the four sides which will be discussed in the nextsection.

The second step is to use if possible “stub plates” illustrated at 121in FIGS. 9A-9C. These “stub plates” electrically connect directly tonothing save the overlying electrodeposited terminal 122.

The third step is to deposit copper followed by nickel onto the exposedelectrodes. Electroless copper will be deposited as a seed layer toallow the nickel to be electrodeposited. The key to the EDT method islateral growth of the nickel deposit. Lateral growth is essential inorder to electrically connect the electrodes, as shown in FIG. 10A andFIG 10B.

2. Advantages of EDTCs over Standard Capacitors

As discussed in Section 2.5 of the Background of the Invention sectionof this specification, the conventional method to produce capacitorsuses cermet terminals followed by nickel and tin-lead plating. The EDTmethod of the present invention eliminates the thick film step and goesdirectly to plating. By eliminating the thick film step, there is asignificant cost savings both in terms of materials and in terms ofprocessing time. It is difficult to estimate the cost savings. In orderto make a precise estimate it would be necessary to know the coststructure of the industry in detail, and manufacturers generally do notpublish this information. However, for manufacturers who producemillions of capacitors per day, the elimination of a process step andthe associated labor and capital equipment would represent a significantcost saving.

Aside from the cost savings for the manufacturers, a greater advantagemay be realized by the users. A key factor in modern electronics is thedrive to make circuits as small as possible, therefore it is importantto make efficient use of available board space. The conventional MLCC,by its design, necessitates a certain amount of wasted board space. FIG.11A and FIG. 11B are a general side view of mounted ceramic capacitors.FIG. 11C shows two standard capacitors next to each other with a gap inbetween. The gap is necessary in order to prevent the two componentsfrom electrically shorting, as shown in FIG. 11D. FIG. 11E shows twoEDTCs next to each other without a gap and without shorting, thus savingthe space that was occupied by the gap. Additional modifications to theelectrode configuration may be possible to manufacture EDTCs that couldbe placed end to end without shorting.

3. Disadvantages of EDTCs over Standard Capacitors

It is likely that this method can only be used on parts with electrodespacings less than some maximum distance, which will be discussed infollowing Section 5.2. In FIG. 10A and FIG. 10B the thickness of thenickel deposit is shown to be proportional to the electrode spacing.Plated nickel deposits tend to exhibit some degree of internal stress.See Dini, J. W., Electrodeposition, The Materials Science of Coatingsand Substrates, Noyes Publications, New York, 1993. The resultant forcefrom this stress increases with the thickness of the deposit. Adhesionof the deposit to the capacitor could degrade as discussed in Section2.8 of the Background of the Invention section of this specification.

Another disadvantage is that the two sided wrap-around configuration mayrequire tooling changes in order to be handled by automated equipmentthat have been designed to handle four sided parts.

4. Fabrication Procedures

4.1 Introduction

The preferred fabrication procedures in accordance with the presentinvention are divided into four main sections. First are the platingprocedures for electroless copper, electrolytic nickel, and electrolytictin-lead. Second is cross-sectional inspection of the plated parts.Third is terminal strength evaluation. Fourth are electricalmeasurements.

4.2 Test Parts

The ceramic multi-layer capacitor bodies used in the preferred procedureare a common industry type as appears, among other places, in thecapacitors of Presidio Components Inc. of San Diego, Calif., assignee ofthe present invention. In description of the parts the size code was0403. The nominal dimensions are 1.0 mm×0.75 mm×0.50 mm (0.040inch×0.030 inch×0.020 inch). The ceramic dielectric is X7R. Theelectrodes are 30% palladium-70% silver. The nominal capacitance is 56nF. The rated working voltage is 12 VDC.

4.3 Plating Procedures

A summary of the preferred plating procedures is shown in Table 1 ofFIG. 12B. The main steps are explained in the following sections.

4.3.1 Activation

Prior to electroless plating it is necessary to clean and activate thesurfaces to be plated. The parts were rinsed with isopropyl alcohol toremove any oil and grease. A 10% hydrogen peroxide (H₂O₂) solution wasused as an activator. The parts were immersed in the solution for 2minutes. The electrodes to be plated are composed of 70 percent byweight silver and 30 percent by weight palladium. The high Ag contentmakes H₂O₂ an appropriate activator. See Rudy, F. S., SurfacePreparation of Various Metals an Alloys Before Plating and OtherFinishing Applications, Metal Finishing Guidebook and Directory, 2001,p. 191-205.

Hydrogen peroxide activates the electrodes only and not the ceramic.Conventional activators for plating on ceramics, such as SnCl₂ andPdCl₂, could not be used since they would have allowed the copper todeposit onto the entire capacitor, including the ceramic surfaces.

4.3.2 Electroless Copper

4.3.2.1 Solution Preparation

A preferred electroless copper solution, Enplate CU-406, is manufacturedby Ethone OMI. The operating conditions and solution make-up, outlinedbelow, are prescribed by Enthone. See Enthone OMI Inc., ENLATE Cu-406Electroless Copper Plating Solution for Printed Wiring Board Processing,Enthone Technical Data Sheet, 1995.

As with many commercially available plating solutions, the manufacturerkeeps the composition of the solution proprietary. One liter of solutionwas prepared for the plating procedure. The solution was prepared byadding approximately half the necessary amount of DI water to thebeaker. Next, 100 ml of CU-406A, 100 ml of CU-406B, and 10 ml of CU-406Cwere added in order. Last, the balance of the DI water was added.

The operation conditions are 21° C. to 29° C. with mechanical agitation.

The solution make-up is-DI water, 79% by volume; Enplate CU406A, 10% byvolume; Enplate CU-406B, 10% by volume; and Enplate CU-406C Improved, 1%by volume.

4.3.2.2 Apparatus and Procedure

The preferred electroless copper plating apparatus of the presentinvention diagrammed in FIG. 12A requires that parts be placed in thebasket and immersed in the beaker. A magnetic stirrer keeps the solutionmildly agitated, and a thermocouple is used to verify solutiontemperature.

This preferred procedure occurs as per Table 1 of FIG. 12B, and isintended to produce a seed layer of copper in the area of the exposedelectrodes. Parts were immersed in the copper solution with mildagitation for 40 to 45 minutes at room temperature. The parts wereshaken every 2-3 minutes to insure uniform deposit of the copper. Theshaking action allowed the parts to be uniformly exposed to the platingsolution.

4.3.3 Electrolytic Nickel

4.3.3.1 Solution Preparation

The nickel bath is the conventional nickel sulfamate bath as outlined byDiBari. See DiBari, G. A., Nickel Plating, Metal Finishing Guidebook andDirectory, 2001, p. 270-288. The bath was prepared by first addingapproximately half the necessary amount of DI water to the tank. Thennickel sulfamate, nickel chloride, and boric acid were added in thespecified concentrations. The balance of the DI water was added, thebath was brought to temperature, and the pH was verified.

The operating conditions were as follows: Nickel sulfamate, Ni(SO₃NH₂)₂, 4H₂O 315 g/l to 450 g/l; Nickel chloride, NiCl₂, 6H₂O 0 g/l to 22g/l; Boric acid, H₃BO₃ from 30-45 g/l. The temperature in ° C. was50°±5°; the agitation mechanical; the pH 4±0.5; and the sacrificialanodes nickel.

4.3.3.2 Apparatus

A preferred set-up for realizing electroless plating in accordance withthe present invention uses a plating tank, most typically a 75-literpolypropylene tank containing 60 liters of plating solution. A ProcessTechnology, model T2217-P1, stainless steel heater is used fortemperature control, and a Filter Pump Industries, model AB1R017N#,circulating pump is used for solution agitation. The rectifier withamp-minute counter is manufactured by HBS Equipment Corporation, modelM259N-5. Plating barrel is Sterling, model HD24-Super, with a 300 mlbasket. During operation, the basket is rotated at 10 rotations perminute. The basket was loaded with 120 ml of conductive ball media. Theball media are stainless steel, 0.5 mm nominal diameters. The mediacomprise approximately 1 m² of surface area.

4.3.3.3 Procedure

This step is intended to grow a layer of nickel on top of the copperseed layer. The apparatus for this electrolytic plating is the same asis shown in FIG. 6. The plating conditions were 600 amp-minutes at 10amps for 60 minutes of plating time. The current density is 10 amps persquare meter. At the end of the 60 minutes the parts basket was rinsedthoroughly with the parts and plating media inside. After rinsing theplating barrel was immersed in the tin-lead bath for tin-lead plating.

4.3.4 Electrolytic 90-10 Tin-Lead Solder

4.3.4.1 Solution Preparation

The tin-lead bath, Solderon LG, is manufactured by LeaRonal, and thebath was prepared as prescribed by LeaRonal. See LeaRonal Corp.,Solderon LG Tech Spec 47460, 1989. Half the necessary amount of DI waterwas added to the tank followed by Solderon LG Makeup, Solder LG TinConcentrate, and Solderon LG Lead Concentrate in the appropriateconcentrations. The balance of the DI water was added, and the pH wasverified.

The operating conditions were as follows: Tin 12-18 g/l; Lead 1.5-2.5g/l; temperature in ° C. 24°±3°. The agitation was mechanical; the pH3.5±1.0; and the sacrificial anodes were 90%-10% tin-lead.

The solution make-up was Solderon LG Makeup 50% by volume; Solderon LGTin Concentrate 15% by volume; Solderon LG Lead Concentrate 2% byvolume; an DI water for the balance.

4.3.4.2 Apparatus

The apparatus for electrolytically plating tin-lead is similar to thatfor electrolytically plating nickel, as shown in FIG. 6 and justdescribed in Section 4.3.3.2. There are two obvious differences: thesolution and the sacrificial anodes. The anodes for plating tin-lead arepreferably 90%-10% tin-lead solder.

4.3.4.3 Procedure

Tin-lead was plated onto the parts in order to make the part easilysolderable. This is necessary for the terminal adhesion test, which willdiscussed in following Section 4.5. The plating conditions were 300amp-minutes at 3 amps for 100 minutes of plating time. The currentdensity is 3 amps per square meter.

4.3.5 Final Cleaning

The parts and ball media were separated, and the parts were then rinsedthoroughly with DI water and dried. Multiple rinses with DI water arenecessary to completely remove the plating solution from the capacitors.Ionic residue on the parts can lead to poor dissipation factor andinsulation resistance measurements.

4.4 Cross-Sectional Inspection

A number of samples were cross-sectioned in order to inspect the ceramicto plated deposit interface. Parts with copper only, Cu—Ni, andCu—Ni-tin-lead were cross-sectioned. Both optical microscope and ascanning electron microscope (SEM) were used to inspection. The opticalmicroscope is a Nikon, model 64438, and the SEM is a LEO, model 438VT.

4.5 Terminal Strength Evaluation

A pull test was performed to evaluate the adhesion of the plateddeposits to the ceramic capacitors. Due to the mounting method used forthis test, only tin-lead plated parts were tested. The parts weresoldered to copper wires and attached to a force gauge. An increasingtensile load was applied, and the load at which the part broke wasrecorded. The force gauge was manufactured by Extech Instruments, model475040.

4.6 Electrical Evaluation

Electrical measurements were made for four groups of parts withdiffering terminals. Groups 1 and 2 are parts with conventional Agtermination. Group 1 is un-plated, and group two is plated with nickeland tin-lead. Groups 3 and 4 are the EDTCs with Ni only and with Ni andtin-lead, respectively. A summary of the electrical tests will bediscussed in the following sections.

4.6.1 Capacitance and Dissipation Factor

Capacitance and Dissipation Factor (DF) were measured using aHewlett-Packard (i) 1 kHz/1 MHz capacitance meter, model 4278A and (ii)a test fixture, model 16334A. The test fixture is a pair or tweezerselectrically connected to the capacitance meter, and to make ameasurement the capacitor under measurement is held with the tweezers.Measurements were made at room temperature with capacitance meter set at1 VAC RMS.

4.6.2 Insulation Resistance

Insulation resistance at 25° C. was measured using a Beckman Industrialmegohmmeter, model L-12. Measurements were made at room temperature withthe megohmmeter set at 12 VDC. Then the parts were placed in an oven setat 125° C., while the megohmmeter remained at 12 VDC.

4.6.3 Dielectric Strength

The parts were tested to failure using a variable DC power supply. Thevoltage was increased from 0 VDC at a rate of 100 VDC per second, andthe voltage at which failure occurred was recorded.

4.6.1 Capacitance and Dissipation Factor

Capacitance and DF were measured and recorded on 50 pieces for each ofthe four groups. Capacitance and DF were measured using a HewlettPackard 1 kHz/1 MHz capacitance meter, model 4278A with test fixture,model 16334A. The test fixture is a pair of tweezers electricallyconnected to the capacitance meter. To make a measurement a capacitorunder test is held with the tweezers.

4.6.2 Insulation Resistance

Ten pieces from each group were measured using a Beckman megohmmetermodel L-12. The applied DC bias was 12 volts. This is the rated workingvoltage of the parts. The megohmmeter uses test tweezers similar tothose of the capacitance meter, and the measurement is made similarly.

4.6.3 Dielectric Strength

Ten pieces from each group were tested to failure using a variable DCpower supply to slowly increase the bias across the part to inducefailure. The voltage was increased at approximately 100 VDC per second,and the voltage at which failure occurred was recorded.

5. Results and Discussion

5.1 Introduction

In Section 3.1 of this specification disclosure, three main challengesfor producing electrodeposited terminals were outlined: selectivedeposition, adhesion strength, and electrical reliability. Selectivedeposition of the EDT of the present invention was achieved by using acombination of (i) electroless deposition of, preferably, copper,followed by, most preferably, (ii) electrolytic deposition of,preferably, nickel.

To address the issues of adhesion and reliability mechanical andelectrical measurements of the EDTCs and standard silver terminal partswere made. All the capacitors measured were from the same batch ofMLCCs.

5.2 Electrodeposited Terminals (EDTs)

The EDT consisted of three layers of plating: electroless copper seedlayer, electrolytic nickel, and electrolytic tin-lead. A series ofcross-sectional micrographs showing the electroless Cu seed layer isshown in FIGS. 13A-13D. The copper tended to be thin, spotty, andconcentrated at the electrodes. The thickness of the copper deposit isestimated at 0.1-0.2 μm. The distance between electrodes isapproximately 10 μm.

On top of the copper seed layer, a layer of nickel was electrolyticallydeposited to form the EDT. The micrographs of FIGS. 14A-14D show thatthe copper seed layer has been completely covered by a continuous layerof nickel. Lateral growth, as discussed in Section 3.5, of the nickeldeposit is essential in forming a continuous deposit that connects allthe electrodes together. In FIG. 14D and FIG. 15 it can be seen that anickel deposit of 2-4 μm can have lateral growth on the order of 10 μm.

Plated nickel deposits tend to develop some degree of internal stress asthe deposit increases in thickness. Many factors affect the internalstress of the deposit including: bath composition, impurities, andcurrent density. See Dini, J. W., Electrodeposition, The MaterialsScience of Coatings and Substrates, Noyes Publications, New York, 1993,supra. To limit internal stress, the maximum spacing between electrodesshould be restricted. Using Smith and Womack's 10 μm as a guideline, theelectrode spacing should be limited to 25 to 50 μm. This should beinvestigated empirically in a further study. In addition, the rate ofdeposition, for both thickness and lateral growth, is strongly dependenton current density. The current density used for the nickel deposit waschosen to form deposits which would be similar to the standard capacitorshown in FIG. 1. A study of current density versus rate of deposit andadhesion strength would be needed to better determine the criticalelectrode spacing.

A Cross-sectional micrograph showing the nickel deposit is shown in FIG.15. The wavy profile of the nickel deposit was expected, as shown inFIG. 15.

Approximately 8 to 10 μm of tin-lead was plated over the nickel, asshown in FIGS. 13A-13D. Micrographs showing a deposit of 90/10 tin/leadover nickel are shown in FIGS. 16A-16D. The nickel and tin-lead depositsare very similar to the deposits shown in FIGS. 4A and 4B. The tin-leadallows the capacitors to be easily soldered so that the terminaladhesion test may be performed.

5.3 Terminal Strength

A comparison of the terminals shown in FIG. 3 and FIG. 16 shows that theEDTs in accordance with the present invention have approximately 30%less contact area to the ceramic than the conventional terminal. Withless contact area, it is appropriate to expect lower terminal strength.A summary of the terminal adhesion test is as follows. The averageterminal strength for the EDTCs is approximately half that of thestandard capacitors. The standard capacitors have plated Ag terminals.Although there seems to be a 50% decrease in terminal strength, in allthe parts tested the failure mode was ceramic fracture and notdetachment of the metallization. This indicates that adhesion of theEDTs is greater than the tensile strength of the ceramic. Consideringthe size of the cap, 600 grams of pull strength appears to be adequate.The difference in pull strength data between the EDTCs and standardcapacitors may be attributable to the difference in terminal geometry.The two side wrap-around may be causing the ceramic to fracture at alower tensile load.

The standard deviation is on the order of 30-50% of the average pullstrength. The ceramic parts were quite fragile and in several casesfailed on the order of 200 to 300 grams. This resulted in a wide spreadof the data. Thus, the estimated error in the measurements is also onthe order of 30-50%. For standard silver terminals plated with Ni andSb—Pb, pull strength ranged from 578 to 1441 grams, with an average of1278 grams at a standard deviation of 451 grams. For electrodepositedterminals of Ni over Sb—Pb, the pull strength ranged from 357 to 1002grams, with an average of 643 grams at a standard deviation of 318grams.

5.4 Electrical Performance

Capacitance for the EDTCs was nearly identical to the capacitance of thestandard parts. The plated deposit makes electrical connection to allthe electrodes. The non-contact of some electrodes would have resultedin lower capacitance than was measured. Estimated error for thecapacitance measurements is on the order of 0.1 pF.

Dissipation factor for the EDTCs were also nearly identical to those ofthe standard parts. This shows that the plated deposits made excellentelectrical connections to the electrodes. The EDTCs and the standardcapacitors originated from the same batch of MLCCs. Thus, the onlyfactor affecting DF that is not in common is electrode to terminalconnections. Poor connections would have increased the ESR and wouldhave resulted in higher DF measurements. The DF measurements have anestimated error on the order of 0.1%.

FIG. 15 shows intimate contact between the plated deposit and theelectrodes since no gaps are visible between the nickel and electrodesor ceramic. When compared to the standard capacitor shown in FIG. 3 theelectrode to terminal connections appear identical.

There were no significant differences in the measurements for insulationresistance and dielectric strength. This shows that there was nosignificant degradation of the ceramic and indicates that the EDT methodcan produce electrically reliable parts. The IR measurements haveestimated errors on the order of 10%. The power supply used fordielectric strength increases the voltage at 100 VDC per second andsamples the data at 3 times per second. This equates to a measurementerror of approximately 33 volts.

A summary of data for capacitance, dissipation factor, insulationresistance, and dielectric strength is given in attached Appendices Bthrough D.

6. Conclusions

The goal of the present invention was to develop a process ofterminating multilayer ceramic capacitors using an electroplatingprocesses employing commercially available plating solutions. Acombination of electroless copper and electrolytic nickel was found tobe successful. By depositing a seed layer of copper followed by adeposit of nickel, it was possible to grow the terminals onto MLCCs.

The adhesion of the plated deposit was shown to be approximately halfthat of the adhesion of the standard Ag terminals. Lower adhesionstrength was primarily due to reduced contact area to the MLCC. However,the adhesion strength should more than suffice for attachment processes.

Electrical performances for the EDTCs were virtually identical to thoseof the parts with standard silver terminals. This shows that the EDTmethod produced terminals with excellent electrical connections to theelectrodes without degradation to the ceramic dielectric.

7. Extensions

In accordance with the preceding explanation, variations and adaptationsof the electroless deposition of terminals to ceramic capacitors, and tomultilayer ceramic capacitors, in accordance with the present inventionwill suggest themselves to a practitioner of the electrical componentarts.

For example, a detailed study of the critical electrode separation,being the maximum allowable separation between electrodes with which theelectrodeposited terminals of the present invention can be used, wouldbe useful. A study of current density versus rate of deposit andadhesion strength would be needed to better determine the criticaldistance between the electrodes.

It is also possible to further investigate potential enhancements toterminal adhesion by heat treating the terminals to promote diffusionbonding between plated deposit and electrodes. A heat treatment processwould need to be carried out in an inert or reducing atmosphere toprevent oxidation of the plating. This process should produce diffusionbonding between the nickel and the electrodes. However, excessivediffusion must be avoided since it would likely result in loss ofelectrical connection or cracking of the MLCC.

In accordance with these and other possible variations and adaptationsof the present invention, the scope of the invention should bedetermined in accordance with the following claims, only, and not solelyin accordance with that embodiment within which the invention has beentaught.

1. A ceramic capacitor comprising: a plurality of interior plates havingedges that are brought to and exposed upon a first surface and havingtheir edges also brought to and exposed upon a portion of a secondsurface of the capacitor at a region where the second surface meets thefirst surface; an electrolessly-plated terminal directly in contactwith, mechanically connected to, and electrically connected to an edgeof each of the plurality of interior plates at locations where eachplate's edge is exposed upon the first surface; and theelectrolessly-plated terminal wrapping over the region of the capacitorfrom the first surface onto the portion of the second surface anddirectly in contact with, mechanically connected to, and electricallyconnected to an edge of each of the plurality of interior plates atlocations where each plate's edge is exposed upon the second surface. 2.The multilayer capacitor according to claim 1 further comprising: one ormore electrolytically plated layers on top of the electroless plating.3. A multilayer ceramic capacitor having a plurality of parallelinterior plates brought to, and exposed at, at least one, first, surfaceof the capacitor for purpose of electrical termination, the capacitorcomprising: an electrically-conductive first-metal layer electrolesslydeposited upon the at least one, first, surface of the capacitor, theelectrolessly-deposited layer being (1) each of (1 a) directly incontact with, (1 b) mechanically connected to, and (1 c) electricallyconnected to, the plurality of interior plates where each is exposedupon the first surface, and (2) sufficiently extensive so as toelectrically connect the plurality of plates, theelectrolessly-deposited layer being characterized in that lateral growthof an electrolessly-deposited first-metal has been sufficientlyextensive so as to span from an edge, exposed at the first surface, ofone of the plurality of interior plates to an exposed edge of a next oneof the plurality of interior plates that is likewise exposed at thefirst surface, the electrolessly-deposited metal thus serving toelectrically connect the interior plates.
 4. The multilayer capacitoraccording to claim 3 wherein the plurality of parallel interior platesare also brought to, and exposed at, a portion of at least one secondsurface of the capacitor at a region where this second surface meets thefirst surface; wherein the electrically-conductive layer iselectrolessly-deposited not only upon the first surface so as to (1 a)contact, and to (1 b) mechanically connect, and to (1 c) electricallyconnect the plurality of plates, but also so as to wrap over a cornerfrom the first surface onto the portion of the at least one secondsurface where the electrolessly-deposited electrically-conductive layeragain also (1 a) contacts and (1 b) mechanically connects and (1 c)electrically connects to the plurality of plates.
 5. The multilayerceramic capacitor according to claim 3 wherein theelectrolessly-deposited electrically-conductive first-metal layerconsists essentially of: copper (Cu).
 6. The multilayer ceramiccapacitor according to claim 3 wherein the electrolessly-depositedelectrically-conductive first-metal layer consists essentially of:nickel (Ni).
 7. The multilayer ceramic capacitor according to claim 3wherein the electrolessly-deposited electrically-conductive first-metallayer consists essentially of copper (Cu); in combination with nickel(Ni).
 8. The multilayer ceramic capacitor according to claim 3 that, ontop of the electrolessly-deposited electrically-conductive layer,further comprises: a second-metal layer of electrically-conductivesecond metal.
 9. The multilayer ceramic capacitor according to claim 8wherein the second-metal layer is plated.
 10. The multilayer ceramiccapacitor according to claim 9 wherein the plated second-metal layer isso plated by process of electroless deposition; wherein theelectrolessly-deposited second-metal layer is characterized in thatlateral growth of the electrolessly-deposited second-metal has beensufficiently extensive so as to cover the electrically-conductivefirst-metal layer that was also electrolessly deposited.
 11. Themultilayer ceramic capacitor according to claim 10 wherein theelectrolessly-deposited electrically-conductive second-metal layerconsists essentially of nickel (Ni).
 12. The multilayer ceramiccapacitor according to claim 12 wherein the plated second-metal layer isso plated by process of electrolytic plating.
 13. The multilayer ceramiccapacitor according to claim 12 wherein the electrolytically-platedelectrically-conductive second-metal layer consists essentially ofnickel (Ni).
 14. The multilayer ceramic capacitor according to claim 8that, on top of the electrically-conductive second-metal layer furthercomprises: a third-metal layer of electrically-conductive third metal.15. The multilayer ceramic capacitor according to claim 14 wherein thethird-metal layer is plated.
 16. The multilayer ceramic capacitoraccording to claim 15 wherein the plated second-metal layer is so platedby process of electrolytic plating.
 17. The multilayer ceramic capacitoraccording to claim 16 wherein the electrolytically-platedelectrically-conductive third-metal layer consists essentially of tin(Sn); in combination with lead (Pb).
 18. A method of electricallyconnecting a plurality of interior plates of a multilayer ceramiccapacitor as, and where, edges of these plates are exposed upon at leastone, first, surface of the ceramic capacitor, the method comprising:electrolessly depositing a layer of conductive first metal directly ontothe at least one surface including where the edges of the plates areexposed.
 19. The method according to claim 18 wherein the electrolesslydepositing of the layer of conductive first metal is further, and also,onto at least a portion of at least one second surface of the capacitorwhere this second surface meets the first surface and where the interiorplates are also exposed.
 20. The method according to claim 18 whereinthe electrolessly depositing is of a layer of conductive first metalconsisting essentially of: copper (Cu).
 21. The method according toclaim 18 wherein the electrolessly depositing is of a layer ofconductive first metal consisting essentially of: nickel (Ni).
 22. Themethod according to claim 18 wherein the electrolessly depositing is ofa layer of conductive first metal consisting essentially of: copper(Cu); in combination with nickel (Ni).
 23. The method according to claim18 further comprising: depositing on top of the electrolessly-depositedelectrically-conductive first-metal layer a second-metal layer ofelectrically-conductive second metal.
 24. The method according to claim23 wherein the depositing of the second-metal layer ofelectrically-conductive second metal comprises: plating.
 25. The methodaccording to claim 24 wherein the plated depositing of the second-metallayer of electrically-conductive second metal comprises: electrolesslydepositing.
 26. The method according to claim 25 wherein theelectrolessly depositing is of an electrically-conductive second-metallayer consisting essentially of nickel (Ni).
 27. The method according toclaim 24 wherein the plated depositing of the second-metal layer ofelectrically-conductive second metal comprises: electrolyticallydepositing.
 28. The method according to claim 27 further comprising:depositing on top of the electrolytically-depositedelectrically-conductive second-metal layer a third-metal layer ofelectrically-conductive third metal.
 29. The method according to claim29 wherein the depositing of the third-metal layer ofelectrically-conductive third metal comprises: plating.
 30. The methodaccording to claim 29 wherein the plating of the third-metal layer ofelectrically-conductive third metal comprises: electrolytically plating.31. The method according to claim 30 wherein the electrolyticallyplating is of an electrically-conductive third-metal layer consistingessentially of tin (Sn); in combination with lead (Pb).